Alpine PDX 4.100

An extremely compact advanced design of Class D digital amplifier. Said to achieve similar results to Class AB amps but in a much smaller space. Three PDX amps (all of which have the same footprint) may be stacked one atop the other using the removable disc feet system and the supplied bolts. It looks very clean and smart with brushed black alloy panels and a set of controls that is hidden until you remove the Allen-bolt secured panel. Underneath is a gain potentiometer (screw-headed knob) for each pair of channels. A crossover switch for each pair of channels may be set to HPF/LPF (high pass or low pass) or Off and the 12dB per Octave slope crossovers can be set between 30Hz and 400Hz so are intended for use with subwoofers, or else to filter out the very deep lows from a set of components. The speakers connect via a new proprietary Alpine speaker plug system that cannot be cross-polarity connected once the wires have been fixed in via the Allen-headed grub screws within them. The power terminals are a robust design with solid Gold plated brass blocks set at an angle to make connection and disconnection easier. The hex wrenches (Allen Keys) are supplied too. A large panel glows blue in the middle of the top when it is on. Echoed by a blue lamp on either end of the panel under which the controls normally hide on the flank of the amp. You need no ‘Y’ leads with this amp if you have just one RCA feed to the thing as you can assign the inputs to appear at the other pair of RCAs should you need to. It stays at the fixed 100 watts output per channel even if the impedance of the speaker load varies as can be seen by the specifications below. You bridge the amp by using one side each (positive or negative) of two speaker connector plugs.
– Class D Full Range
– 4 x 100w RMS @ 4 Ohms
– 4 x 100w RMS @ 2 Ohms NB: The same as 4 Ohms
– 2 x 200w RMS @ 4 Ohms bridged
– Aluminium panel heatsink with stack system for stacks up to three deep
– Adjustment controls hidden under a metal plate with Allen headed retainer bolt
– 8Ga. Power Terminals with Allen headed grub screw bare wire socket connection
– High cable diameter speaker connection plug and socket system
– Adjustable input sensitivity: 0.2V to 4.0V
– Square blue illuminated power on indicator on top plus two other paired channel status indicators
– Stereo & bridged operation
– Frequency response 20Hz to 20kHz
– Signal to Noise Ratio 96dB
– High/Low Pass Filters one per pair of channels – 30Hz to 400Hz (@12dB per Octave)
– Fuse Rating 30A x2
– HxWxD(mm) 62 x 257 x 192mm
Review by Adam Rayner
The PDX range looks to be aimed at the potential amplifier buyer who really doesn’t want amps. This buyer wants the results but isn’t too troubled about it looking flash. Under the seats is just fine. However, if you are a brand-o-phile and want to make a Big Deal out of your amplifier install and also wish to have some serious power on board, the stacking feature will impress you. They are very good looking in fact. Taking a nice idea from the world of hifi, where most things have the same footprint and thus stack nicely, these units have ‘hifi’ feet. Small metal discs and corresponding recesses underneath them. You either leave the discs in place and just use the amp as it is, or you can remove these discs, called Joint Caps. You bolt your amplifier down, then you can fit the joint caps and screw another amp to them, fitting into the recesses underneath. Do it twice and you can have the three amp stack.
The controls are completely hidden under a full-width metal plate held on with an Allen headed bolt. You get a gain control, crossover point selection knob and switchable crossover for each pair of channels and a switch to direct the input to the other channels too. This is great if you have a cheap deck with only one RCA out or you want to use lots of amps. The speakers are connected by a modular plug thing that bears a striking resemblance to the USB plug system. It’s a bit clunky but it can take huge or small diameter speaker wires, crimping down on them with a metal plate driven by an Allen headed grub screw system inside. The inner conductor of this plug does the (+) feed, the outer conductor the (-). So if you want to bridge, you just do it as normal. Which means the (+) wire goes into the (+) terminal of one speaker plug and the (-) into the corresponding side of the other channels’ plug.
It is a class D design, and the blurb goes on about how this is as good as any class AB amplifier. It does have a creditable 96dB signal to noise ratio. I fired it up and was taken by the lovely modern Blue LED illumination. Both a slabby blue bit on the top and a nice slice on each side. In testing I did something stupid and managed to make one pair of channels go into protect. The glowing slice on the end went red and didn’t go blue again until I had powered down and started again.
The sound is big and the use of current is impressively efficient. My world rocked louder on the limited power I was using, more than any other yet. If you have issues with alternator power or the lack of a decent margin and you are a hooligan, this is a Bloody Brilliant Product. I did find it a bit less sweet and open than their best analogue designs but that says more about Alpine. That the company that uses Microdynamics (A mad level of attention to detail and component matching and stuff) makes an amp that sounds incredible isn’t really the point. This is clearly the best class D amp I’ve clapped ears on. The bridging thing is less than obvious and although it would be hard to fit it on a small graphic of how to bridge might be an intelligent addition to the inside of that removable panel. I called them up and had to have them show me on the manual sheet where it is explained. Which yet again reveals only my lack of urge to RTFM!
A powerful piece of technology that looks very smart and works well. Awesome for windows-down-o-choon merchants but not the model a dyed-in-the-wool audiophile would buy.
Overall 8.2
Sound Quality 8
Power Output 8
Features 8
Build Quality 9
Value For Money 8